The agreement was established in support of objective 4 of the in-house project, which is to investigate the impacts of vineyard practices on soil microbial ecology. The project's goal is to develop "in-row" weed management practices that both provide effective weed management, do not negatively impact grapevine growth and juice, and improve soil nitrogen retention by minimizing inorganic nitrogen leaching and nitrous oxide emissions.
The establishment of ‘in-row’ treatments was initiated in October of 2009. Greenhouse gas emissions (nitrous oxide, N2O and carbon dioxide, CO2) were collected bimonthly, and carbon (C) and nitrogen (N) dynamics in response to events that increase greenhouse gas emissions were measured from October 2009 to the present. These measurements continued until December 2011. The biweekly measurements for inorganic nitrogen pools, soil water content and temperature, and greenhouse gas emissions were completed. All soil samples that were collected have been assessed for nutrient content. Weed communities, grape yield, harvest characteristics and pruning biomass were characterized. Necessary reports were issued to the funding agency. The data are currently being analyzed. Findings indicate that ‘pulse’ events such as cultivation, compost addition, fertigation, irrigation and rainfall are major periods of greenhouse gas emissions. When cultivation occurred just after compost addition, N2O and CO2 emissions increased and were greater than the cover crop and herbicide treatments. When rainfall occurred immediately after this cultivation, N2O and CO2 emissions were also greater than the other treatments, highlighting the interactive effects of management (i.e., cultivation and compost) and rainfall on greenhouse gas emissions. When treatments were irrigated, both N2O and CO2 were greatest from the cultivated treatment, followed by the cover crop and herbicide treatments, respectively. Although the cultivated treatment emitted more GHGs, further analysis will determine the net carbon footprint of each respective treatment. The cover crop and herbicide treatments tended to have greater nitrate leaching than the cultivated treatment. Grape juice characteristics such as pH, titratable acidity, yield, and total soluble solids did not differ among treatments. Temporal dynamics of leaching differed among treatments, suggesting that management practices could be adjusted over time to minimize these losses. Data from this study will be incorporated into the GRACEnet (Greenhouse gas Reduction through Agricultural Carbon Enhancement network) database to develop predictive models of greenhouse gas emissions in response to agricultural management. Furthermore, findings from this study will be included in the development of an interactive process model for grower use assessing GHG emissions associated with different management practices, a project that was awarded to the California Sustainable Winegrowing Alliance by CDFA SCBG (“Field Testing a Carbon Offset and Greenhouse Gas Emissions Model for California Wine Grape Growers to Drive Climate Protection and Innovation”). Outreach will be conducted through the Napa Viticulture Tech Committee and Lodi Woodbridge Grower’s group. Findings have been shared with the grower cooperator and also at the Soil Science Society of America meetings. The progress made on this project has been adequate and meets all expected milestones.